1. Field of the invention:
This invention relates generally to pumping assemblies for well servicing applications, and in particular to a pump assembly comprising two pumps mounted back-to-back on a trailer or skid.
2. Description of the Prior Art:
Oil and gas wells require servicing such as cementing, gravel packing, and acidizing. All of these services require pumps for pumping fluid down the well.
The type of pump used normally for these applications is a plunger type. It has a crankshaft mounted in a housing. A plunger has a cross head that is reciprocally carried in a cylinder perpendicular to the crankshaft. A connecting rod connects each eccentric portion or journal of the crankshaft to the plunger. A typical pump will be a triplex type having three cylinders, three connecting rods, and three journals on the crankshaft. Normally the axis of rotation of the crankshaft will be intersected by the axis of the cylinder. A diesel engine or other prime mover will connect to a gear train for rotating the crankshaft.
Often these pumps will be mounted on a trailer or skid back-to-back. Each pump has an outboard side connected to a manifold with valves for drawing in and pumping fluid acted on by the plunger. The inboard sides will be located next to each other. A separate prime mover or engine will be connected to each of the pumps.
The overall width from the one manifold to the other manifold should not exceed roadway requirements if the pumps are to be trailer mounted, this being about 81/2 feet. This overall width requirement constrains the size of the pumps. Typically the stroke of the plunger can only be four inches in order to meet the 81/2 foot space requirement.
It has been known in the past with larger oil field pumps for different applications to increase the stroke by offsetting the crankshaft axis with the cylinder axis. The offset is selected so that during the power or output stroke, the centerline of the crankshaft end of the connecting rod will be located closer to the cylinder axis than the crankshaft axis. As far as is known to Applicant, pumping assemblies with pumps back-to-back as described above have not had vertical offsets.